This section provides background information related to the present disclosure which is not necessarily prior art.
Wireless network infrastructure has been evolved to the needs to enhance capacity and throughput of the wireless application devices, such as laptop computers, cellular phones, etc. Consequently, multiple frequency bands and multiple antennas (e.g., Multiple Input Multiple Output) with higher gain are utilized to accommodate the needs of the wireless network application.
FIG. 1 illustrates a conventional half-wave dipole antenna 100. The antenna 100 includes a radiator element 102 and a ground element 104. The radiator element 102 and the ground element 104 are connected to, and fed by, a signal feed 106. Each of the radiator element 102 and the ground element 104 has an electrical length of about one quarter of the wavelength (λ/4) of a signal at a desired resonant frequency of the antenna. Together, the radiator element 102 and the ground element 104 have a combined electrical length 108 of about one half of the wavelength (λ/2) of signals at one desired resonant frequency of the antenna 100.
In addition, omnidirectional antennas are generally preferable in most applications as they allow for good transmission and reception from a mobile unit in various directions. Generally, an omnidirectional antenna is an antenna that radiates power generally uniformly in one plane with a directive pattern shape in a perpendicular plane, where the pattern is often described as “donut shaped.”
One type of omnidirectional antenna is a collinear antenna. Collinear antennas are relatively high gain antennas that are used as external antennas for wireless local area network (WLAN) applications, such as wireless modems, etc. This is because collinear antennas have relative high gain and omnidirectional gain patterns.
Collinear antennas consist of in-phase arrays of radiating elements to enhance the gain performance. But collinear antennas are limited in that they are only operable as single band high gain antennas and may not be optimum for large bandwidth or multiple frequencies. By way of example, FIG. 2 illustrates a conventional collinear antenna 200 including upper and lower radiator elements 202, 204 each having an electrical length of about one half of the wavelength (λ/2) of a signal at a desired resonant frequency of the antenna 200.
In order to achieve high gain for more than a single band, back-to-back dualband dipoles may be placed on opposite sides of a printed circuit board. For example, FIGS. 3 through 5 illustrate a conventional antenna 300 having back-to-back dipoles such that the antenna 300 is operable over two bands, specifically the 2.45 gigahertz (GHz) band (from 2.4 GHz to 2.5 GHz) and the 5 GHz band (from 4.9 GHz to 5.875 GHz). For this conventional antenna 300, there are an upper pair of dipoles 302, 304 operating on the 2.45 GHz band and two lower pairs of dipoles 306, 308, 310, 312 operating on the 5 GHz band. FIG. 3 illustrates the dipoles 302, 306, 308 on the front of the printed circuit board (PCB) 314, while FIG. 5 illustrates the dipoles 304, 310, 312 on the back of the PCB 314. The antenna 300 also includes microstrip line or feeding network 316 with a power divider to feed and divide the power to each of the various antenna elements.